JPS63119988A - Electric resistance welding method for galvanized steel sheet - Google Patents

Abstract

PURPOSE:To improve the corrosion resistance and welding efficiency of steel sheet by sprinkling and spreading or sticking the increasing agent of electric resistance between steel sheets on the joint of the steel sheets in advance and then, performing the electric resistance welding. CONSTITUTION:The resistance increasing agent 4 made of alumina powder, etc., is interposed between the two steel sheets 7 to which galvanized layers 2 are formed on both surfaces of base metals 3 to form a gap 5 on the mating face of the steel sheets 7. When electrodes 1 are pressed against the steel sheets 7 to perform the electric welding, the electric resistance is high on the mating face, so the temp. of the part become higher preferentially than other parts. At this time, the galvanized layers 2 are first molten and then, the base metals 3 are molten thinly to form a nugget. Since the welding is finished with little current or in a short period of time, the welding efficiency is improved by this method. Further, since the dissipating quantity of zinc of the galvanized layers 2 is reduced, the corrosion resistance of the steel sheets of a welded zone is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to resistance welding, and particularly to improving the resistance weldability of galvanized steel sheets.

(Prior Art) Galvanized steel sheets, in which at least one surface of a steel sheet is plated mainly with zinc, are widely used as materials for the bodies of automobiles and washing machines. These galvanized steel sheets are usually joined by electric resistance welding such as spot welding, projection welding, and seam welding, but galvanized steel sheets have inferior resistance welding properties compared to ordinary steel sheets that do not have a plating layer. . This is because zinc has a relatively low electrical resistance and is soft, so it fits well when the galvanized steel sheets to be joined are pressed together, so the contact electrical resistance of the mating surfaces is small and sufficient heat is generated. This is because it cannot be obtained. Therefore, for example, when spot welding galvanized steel sheets, the welding current and welding time are usually set 25 to 50% larger and the welding time 50 to 100% larger than those for normal steel sheets, resulting in large power consumption. Moreover, the size of the nugget formed by welding is not constant, making the welding strength unstable, and the contact surface between the electrode and the steel plate generates a lot of heat (which causes severe wear and tear on the electrode, and the zinc adhering to the electrode This will inevitably lead to poor productivity and increased costs.

Since the corrosion resistance of galvanized steel sheets is mainly due to the sacrificial corrosion effect of zinc, it is desirable to increase the thickness of the plating layer in order to increase the corrosion resistance.
The above tendency is exacerbated and the resistance weldability becomes even worse.

For this reason, when it comes to materials for automobile bodies, electrogalvanized steel sheets, etc., which have a small amount of zinc deposited even at the expense of corrosion resistance, are often used, except in North America and Northern Europe, where snow melting agents are sprinkled on the road surface. In addition, alloyed galvanized steel sheets, zinc-based alloy coated steel sheets, which have been improved so that good corrosion resistance can be obtained with relatively thin plating layers.
Multilayer galvanized steel sheets are used.

(Problems to be Solved by the Invention) As mentioned above, galvanized steel sheets with relatively thin plating layers generally have excellent resistance weldability, but they are still poor when compared to bare steel sheets without a plating layer. The current situation is that improvements are desired, especially resistance welding of galvanized steel sheets with a large amount of zinc coating, which has excellent corrosion resistance and is used in automobile body steel sheets for North America and Northern Europe, which require excellent corrosion resistance. There is a strong need for sexual improvement. The present invention was made to improve the resistance weldability of this galvanized steel sheet.

Structure of the Invention (Means for Solving Problems) The present invention relates to a galvanized steel sheet in which a plating layer mainly composed of zinc is formed on at least one surface of the steel sheet, and when electric resistance welding is performed with the zinc layer between the sheets. This is a resistance welding method in which a substance to secure a gap between the plates and increase the resistance between the plates, or a poor electrical conductor substance, is applied or pasted to the joining area between the plates in advance.

The substance that is present between the plates to ensure a gap and increase the resistance between the plates, that is, the resistance increaser, is preferably a substance that itself is a poor conductor of electricity, and for example, ceramic powder or the like is suitable. However, even when using a good electrical conductor, it is possible to increase the resistance between the plates by ensuring a gap, so this is not excluded even when using a good electrical conductor.

The present invention can be applied to all galvanized steel sheets. In other words, not only normal double-sided or single-sided galvanized steel sheets, but also alloyed galvanized steel sheets in which the galvanized layer is treated with Fe-Zn alloying to improve adhesion to paint and resistance weldability, and improved corrosion resistance of galvanized steel sheets. Zn-Ni, Zn-Co-Cr, Z
Alloy plated steel sheets such as n-A1-3n series, Z n which not only has improved corrosion resistance but also has improved weldability and press formability.
The present invention can be applied to multilayer galvanized steel sheets such as Zn/Mn series and Zn/Ni series.

Effects of the Invention The resistance welding method according to the present invention is performed by interposing a resistance increaser on the mating surfaces of two galvanized steel plates to be joined to each other. Can be welded with current and short time. Therefore, there is little temperature rise at the contact surface between the electrode and the steel plate, and wear and tear on the electrode is reduced, making it possible to perform stable welding work.

For the same reason, there is less loss of the zinc layer in the indented part that occurs on the surface of the spot weld, and a decrease in rust prevention performance can be avoided.

In addition, since heat generation is concentrated in a limited area of the mating surfaces of the two sheets to be joined, the nugget thickness is reduced, fewer dents and deformations occur during welding, and the heat-affected zone of the base metal is also smaller. Therefore, the strength of the welded part increases. For the same reason, nuggets are less likely to be formed in areas other than the mating surfaces. When spot welding a relatively thin plate and a thick plate, a nugget is formed in the middle part of the thick plate in the thickness direction.
Although there are cases where the intended mating surfaces are not formed, the resistance increaser increases the electrical resistance of the mating surfaces, so that such a situation can be effectively avoided.

The reduction in current not only reduces power consumption, but also shortens welding time, improves welding efficiency, and allows for proper nuggets while avoiding splinters and explosions. The range of appropriate current values that can form a wide welding condition makes it easier to manage welding conditions, resulting in a lower failure rate.

(Example ■) When spot welding is carried out by stacking two hot-dip galvanized steel plates in which a galvanized layer of 60 g per d is formed on both sides of a mild steel plate of plate jE0.8+u by the Dobb method,
The average grain size is 3 in the area where nuggets are to be formed on the mating surfaces.
Six pieces of alumina (AlzOs) powder of 0.0jlm were spread almost evenly and a spot welding test was conducted under the following conditions.

Electrode diameter used: 16mm (tip diameter 61-) Pressure force
: 220Kg Welding current setting value: 11. The OKA experiment was conducted using alumina powder (sample no.

1.2) and when not used (sample No. 3.4.5
．． 6.7). The experimental results are shown in FIG. 1, and the experimental conditions are shown in Table 1.

In Figure 1, the horizontal axis represents the energization time in terms of the number of cycles of welding current, and the vertical axis represents the electrical resistance between the electrodes during welding in the upper row, and the electric resistance value between the electrodes during welding in the lower row. indicates the diameter of the obtained nugget (fusion part).

If alumina is used, energization is carried out for three cycles until a suitable nugget is obtained; if alumina is not used,
The test was extended until a suitable nugget was obtained. In this experiment, when alumina was not used, proper nuggets were obtained after 5 to 6 cycles of current application, but failure occurred in the 7th cycle and the nuggets were defective.

Regarding the dynamic resistance value, the figure shows only the change in the dynamic resistance value for each sample up to 3 cycles when alumina was used, and only for sample No. 6, which was energized up to 6 cycles when no alumina was used. The dynamic resistance curves of sample No. 3.4.5.7 showed similar trends to those of No. 6, so they were omitted.

The current value during welding was slightly different from the set current value, especially at the beginning of welding, and there were also differences between individual samples, so the current value for each cycle was calculated for all samples together with the set current value. The following was shown.

As is clear from the top row of Figure 1, although there is some variation between individual samples, when alumina is used, the initial welding time is significantly lower than when using normal galvanized steel sheets without alumina. The dynamic resistance value is high, and as shown in the lower row, nuggets are formed in a short current application time. That is,
With a normal galvanized steel plate, it takes 5 cycles to obtain a nugget with a diameter of 3.5 mm, and 6 cycles to obtain a nugget with a diameter of 4.0 mm, but when alumina is used, In sample No. 1, a nugget with a diameter of 4.5 cranes was produced by 3 cycles of energization.

The same is true for 2 (a 4.1 dragon nugget was formed with 3 cycles of energization. Even though the current value is approximately the same whether or not alumina is used, the welding time is approximately half that). In addition, when alumina is not used, there is only a margin of about two cycles from the time a proper nugget (in the case of this experiment, the diameter was 3.51 mm or more) is formed until the nugget becomes defective due to expulsion. When alumina is used, there is a margin of about 4 cycles, and in the spot welding method of the present invention, the appropriate current application time or current range is wider than in normal cases.

The effects of the present invention shown in FIG. 1 are believed to be due to the following reasons. As shown in FIG. 2, a resistance increaser 4 made of alumina powder is interposed between two steel plates 7 to be spot welded with a galvanized layer 2 on both the front and back sides of a base metal 3. , a gap 5 is formed between the mating surfaces of both steel plates 7.

Because of this gap 5, when the electrode 1 is pressed against the steel plate and welded, the electrical resistance at the mating surfaces becomes high, heat generation occurs intensely at the mating surfaces, and the temperature of this part becomes higher than other parts.

The galvanized layer 2 first melts at the part where the nugget is to be formed on the mating surfaces where the temperature is highest, then vaporizes, expands, and is expelled to the outside, and the base material 3 is thinly (melted) along the mating surfaces. Therefore, thin nuggets are formed.

As nugget formation progresses, the resistance value decreases.

On the other hand, in the case where alumina is not used, the inter-plate resistance when two galvanized steel plates are stacked is low because the zinc has good compatibility with each other. Therefore, at the initial stage of energization, the amount of heat generated is small and no nuggets are formed. As the current application time increases, the temperature increases over a wide range of the base material due to the so-called volume resistance of the entire base material. As the temperature of the base material increases, the resistance value of the base material also increases, and this increases the amount of heat generated, eventually causing a portion of the base material to melt and form a nugget.

Here, when the nuggets are formed, the base material is at a high temperature over a wide range, so it is in a state where it is easy to scatter even with a slight change in the current value, and the nuggets that are formed are thick. FIGS. 8 and 9 are photographs showing a comparison of sample No. 1 using alumina and No. 5 nugget not using alumina. Nugget diameter is sample N
Even though o and 1 are somewhat large, the thickness of the nugget is extremely small. A smaller nugget means less energy is required for joining, and a narrower heating range reduces deformation, residual stress, and altered parts of the base metal during welding, making it a desirable weld. .

Note that the alumina used may remain in the nugget. However, since the particle size of alumina is small and the amount is small, there is no problem.

On the other hand, the electrical resistance and thermal conductivity at the contact surface between the electrode 1 and the plated steel plate 7 are the same when using the normal spot welding method and when using the resistance increaser 4 interposed between the plates according to the present invention. However, in the latter case, with a small current,
Alternatively, if the current is constant, welding will be completed in a short time, and as a result, the temperature of the plating layer 2 in contact with the electrode 1 will be lower than in the normal method. The temperature distribution between the plates when the resistance increaser 4 is used, as shown by the broken line in FIG. 2, is higher than that when it is not used, as shown by the solid line. The temperature of the plating layer 2 becomes lower. Therefore, the amount of zinc lost from the galvanized steel sheet 7 in the area in contact with the electrode 1 is reduced, and the corrosion resistance is improved.
Reduces electrode wear.

(Example ■) The results of an experiment conducted using mending tape for the purpose of increasing the inter-plate resistance in spot welding of galvanized steel sheets are shown in FIG. 3, and the experimental conditions are shown in Table 2.

Table-2 Setting current value 10.5KA The galvanized steel plate, electrode, and pressing force used in the experiment are as follows.
This is the same as described above. Setting current value is 10.5KA
It is. As shown in Fig. 4.5, mending tape 6 was applied to one of the galvanized steel plates 7 to be spot welded, and spot welding was performed using this surface as the mating surface. Between two steel plates to be welded, the tape should be 0.1mm maximum at the 411I x 4 piece cut out corner.
(The thickness of the tape is 0.1 mm).

The sample was positioned so that the center of the electrode 1 coincided with the center of the cutout, and spot welding was performed. The test was conducted when tape 6 was attached to steel plate 7 (sample No. 8
．． 9) and the normal case without using tape 6 (sample No. 1)
0.11.12.13.14).

Regarding the interelectrode dynamic resistance, if tape is used, all samples are tested, and if tape is not used, sample No.
, 10 only.

The experimental results showed the same tendency as in Example ① using alumina. That is, when the resistance between the plates was increased using tape, the dynamic resistance at the initial stage of welding was high, and spot welding with a nugget diameter of 3.5H was obtained in 3 cycles of current application. On the other hand, when the tape was not used, no nugget was formed after 3 or 4 cycles of current application, and at 5 cycles, one of the two samples had a nugget diameter of 3 mm, but the other one had a nugget diameter. was not formed. Incidentally, a nugget formed by 3-cycle energization of sample No. 8 using a tape is shown as a photograph in FIG.

As with alumina, the nugget thickness is significantly smaller.

(Example ■) The results of an experiment conducted using commercially available salt grains as a resistance increaser are shown in FIG. 6, and the experimental conditions are shown in Table 3.

Table 3 Setting current value 12KA The galvanized steel plate, electric bridge, and pressing force used were as described in Example I. The set current value is 12. It's OK.

Spot welding was performed by placing six salt grains having an average diameter of about 250 μm approximately evenly at the joint between the plates, that is, at the area where the nugget was to be formed (sample No. 15.16). In addition, in this experiment, spot welding experiments were also carried out on the joints of galvanized steel plates after placing salt on them, and then fixing the salt to the galvanized steel plates with spray glue (sample No.
, 17).

On the other hand, in the case where no salt was used, the same test as in Examples ① and ② was conducted (Sample No.

18.19.20).

Even when salt is used for the purpose of increasing interplate resistance, Example I,
The same effect as seen in ■ is seen.

That is, the initial dynamic resistance value was high, and a nugget with a diameter of 4 mm was obtained after 3 cycles of energization. Also, when the salt was fixed to the steel plate using spray glue, the same effect was observed as when using salt alone without using glue, and 3
A nugget diameter of 3.5R was obtained by energizing the cycle. This result shows that the resistance increaser can be fixed to the steel plate using glue even when the powder material is spread, for example when the joint surface is not horizontal but tilted, or when the wind is blowing. This shows that the present invention can be applied without equivalence. Figure 10 shows a photograph of sample No. 8 nuggets using common salt. In this case as well, the nugget is thin.Although common salt is a corrosive substance, most of it evaporates during welding, and even if it remains around the nugget, it is thought to have little negative impact as it can be washed away.

On the other hand, when no salt was used, no nuggets were formed after three cycles of energization, and small nuggets with a diameter of one fin were formed in the fourth cycle, but dispersal occurred in the fifth cycle. In field work, the set current value is often set slightly high for various reasons, but when the set current value is high, the appropriate energization time range is narrow with normal welding methods that do not use resistance increasers. This indicates that it is difficult to obtain an appropriate nugget.

(Example ■) The experimental results were shown in FIG. 7, and the experimental conditions are shown in Table 4, in which a coating film (ordinary paint) of about 15 μm was applied in advance to the joining area between the plates.

Table 4 Setting current value 11 KA The galvanized steel plate, electrode, and pressing force used were as described in Example ①. The set current value is 11. It's OK.

Even when paint was applied between the plates, about 3.80 nuggets were formed after three cycles of energization.

[Brief explanation of the drawing]

Figure 1 shows the experimental results of Example 2, Figure 2 shows a conceptual diagram of the joint part of Example 2, Figure 3 shows the experimental results of Example H, and Figure 4 shows the experimental results of Example H.
The figure shows a conceptual diagram of the joint of Example 2, Figure 5 shows the plan view of Figure 4, Figure 6 shows the experimental results of Example 2, and Figure 7 shows the experimental results of Example 2. Figure 8 is a cross-sectional photograph of the joint of sample No. 1, and Figure 9 is a photograph of the joint section of sample No. 1.
, Figure 10 shows the cross-sectional photographs of the joints of samples No. 5 and 5.
FIG. 11 shows a cross-sectional photograph of the joint of sample No. 8 and FIG. 11 shows a cross-sectional photograph of the joint of sample No. 17. 1... Electrode 2... Zinc layer 4... Resistance increaser 5... Gap 6... Mending tape Patent applicant Toyota Industries Co., Ltd. TA Seisakusho Energization time (-) Energization time (~) 01.284567 Energizing time (~) Energizing time (~) Engraving of vI side (no change in content) Procedural amendment writing method> February 26, 1988 Acknowledgment Secretary Akio Kuroda 2,! Relationship with the case of the person making the amendment: 1.1 of galvanized steel plate, 1.1, 2.1, 2.1, 2.1, Toyota-cho, Kariya City, Aichi Prefecture. Name: 321.
Address: 0582 No. 2 Hatazume-cho, Gifu City, 500 Japan
(65) -1810 (Kin) Fax only 0582
(66)-1339 January 7, 1988 (Shipped on January 27, 1988) 6. Detailed description of the invention in the specification subject to amendment, WJRL description of drawings and drawing 7, Amendment Contents (1) "It is a photograph" written in lines 16 to 17 of page 12 of the statement will be deleted. (2) ``With a photograph'' written in line 9 of page 17 will be deleted. (3) The "photo" listed in line 7 on page 20 will be deleted. (4) "Joint part...photo" written in lines 12 to 15 of page 22 will be corrected as follows. 9 shows the cross section of the joint road body in Material No. 5, FIG. 10 shows the cross section of the joint road body in Material No. 8,
The figure shows a cross-section of the joint road body of document patient 17.

Claims (1)

[Claims] 1. When electrical resistance welding is performed with a zinc layer between the sheets in a galvanized steel sheet in which a plating layer mainly composed of zinc is formed on at least one surface of the steel sheet, the resistance between the sheets is increased. An electric resistance welding method for galvanized steel sheets in which a substance is sprayed, applied, or pasted on the joining area between the sheets in advance. 2. The electric resistance welding method for galvanized steel sheets according to claim 1, wherein the substance that increases the inter-plate resistance is a substance that ensures a gap between the plates.